This invention relates to salt fluxes and more particularly, this invention relates to a salt flux suitable for use in fluxing or purifying molten aluminum.
In the prior references, there is disclosed the use of salt fluxes that are added to molten metal such as molten aluminum to remove inclusions such as oxides from the melt in order to provide an improved metal having superior properties. For example, U.S. Pat. No. 1,841,599 discloses the use of BaO, BaCO.sub.3, NaF, KClO.sub.3 and carbon. The patent discloses that oxides and oxy-salts of barium are particularly effective in reacting with non-metallic impurities in non-ferrous metals such as aluminum. U.S. Pat. No. 3,041,413 discloses the use of carbides of the alkali metals and the carbides of alkaline earth metals, the carbides being dissolved in molten solvents. The patent discloses the use of a fluxing agent such as sodium and potassium halides to aid in the dissolution of the carbides.
U.S. Pat. No. 1,718,917 discloses a composition or flux suitable for welding, brazing or tempering compound, the compound suitable for use upon oily or greasy metallic surfaces without the necessity of cleaning. The flux has the following ingredients: borax, sol-ammerriac, Venetian red, bicarbonate of soda, salt and powdered coke. According to the patent, the coke is used as a reducing agent to prevent oxidation of the metals.
U.S. Pat. No. 1,882,601 discloses a flux for coating welding rods for welding stainless steels. The flux contains 60% calcium fluoride or carbonate, 20% sodium fluoride and 20% carbon, and the ingredients may be varied according to the following: 40 to 80% alkaline earth salt, 15 to 40% alkaline halide flux and 15 to 40% carbonaceous material.
U.S. Pat. No. 1,975,084 discloses a flux composition for use with non-ferrous metals such as aluminum. The flux composition contains equal parts of an alkali metal chlorate, manganese dioxide, a boron compound, calcium fluoride, zinc, manganese, hematite, dolomite and a carbonaceous substance.
U.S. Pat. No. 2,262,105 discloses a flux for use in melting light metals such as magnesium and aluminum. The flux composition has the following ranges: 20 to 50% magnesium chloride, 25 to 40% calcium chloride, up to 30% sodium chloride and potassium chloride and 0 to 5% magnesium oxide.
U.S. Pat. No. 2,479,798 discloses a welding flux for welding ferrous metals. The flux contains parts by weight, 30 to 50 parts sodium carbonate monohydrate, 10 to 30 parts alkali metal pentaborate, 20 to 40 parts alkali metal nitrate, 5 to 20 parts silica, 1 to 10 parts graphite, and 1 to 10 parts oxide of iron or manganese.
U.S. Pat. No. 2,499,827 discloses a welding electrode for cast iron having a flux coating containing 25-50 parts calcium carbonate, 20 to 35 parts calcium fluoride, 0 to 30 parts iron powder, 10 to 30 parts carbon, 1 to 10 parts ferro-25 titanium and 3 to 6 parts bentonite. A binder may be added to this composition.
U.S. Pat. No. 2,626,339 discloses a welding rod for welding copper alloys. The rod is coated with a flux composition composed of 5 to 15 wt. % carbonaceous material, 15 to 45 wt. % metal carbonate, 20 to 60 wt. % metal fluoride, and from 12.5 to 28 wt. % of a binder of sodium and/or potassium silicate.
U.S. Pat. No. 2,900,490 discloses a flux-coated electrode for welding cast iron. The flux is composed of (parts by weight) 25 to 40 parts alkaline earth metal carbonate, 15 to 30 parts alkaline earth metal fluoride, 15 to 30 parts carbon, 3 to 6 parts silicon as ferro-silicon and 2 to 10 parts rare earth metal and/or rare earth metal oxide.
U.S. Pat. No. 4,761,207 discloses a slat-based melting process for melting aluminum scrap. The salt contains chlorides and fluorides of sodium, potassium, magnesium, aluminum, calcium and lithium. According to the patent, carbon or carbon monoxide is used to control oxide concentration.
U.S. Pat. No. 4,983,216 discloses the use of halide salts such as alkaline earth metal halides or alkali metal halides such as Li, Na, K, Mg and Cu chloride or fluorides in melting aluminum scrap.
U.S. Pat. No. 4,030,914 discloses that aluminum drosses are treated under a cover flux of sodium chloride or potassium chloride or mixtures thereof in combination with calcium chloride, the calcium chloride comprising about 1 to 50% of the flux composition.
U.S. Pat. No. 4,365,993 discloses treating lacquer-coated aluminum scrap with a solution of a mixture of halide salts. The mixture is applied to the scrap before the lacquer coating is pyrolyzed, leaving a metal relatively free from oxide inclusions. The preferred flux is a 50:50 mixture of sodium chloride and potassium chloride, with an optional addition of up to 3% of an alkali metal fluoride.
However, in spite of these fluxes and processes, there is still a great need for an economic, low melting point flux that is free from the use of fluorides. It will be appreciated that fluorides are generally ecologically and hygienically unacceptable. It will be noted that certain fluxes are suggested that do not employ fluorides; however, often these types of fluxes are not as effective in separating molten aluminum from dross or in minimizing oxidation of aluminum scrap during or after the melting process. Consequently, such fluxes can result in increased oxidation and greater losses of molten aluminum to dross or skim, seriously affecting the economics of the scrap recovery process.
The subject flux has the advantage that it does not require or contain fluorides and thus is ecologically acceptable. In addition, the flux can be added in-line to sequestor oxides floating to the surface and to minimize skim.